GB1343699A - Coordinate determining system - Google Patents

Abstract

1343699 Position finding; ultrasonic probes INTERNATIONAL BUSINESS MACHINES CORP 28 May 1971 [18 June 1970] 17821/71 Headings H4D and H4J [Also in Division G4] The co-ordinates of a probe on the surface of a sheet of material are determined by timing the passage of ultrasonic waves to the probe from each of two ultrasonic vibration generators coupled to the sheet, the two generators being energized in turn by applied sinusoidal electrical signals. In the Fig. 1 and 2 embodiments the waves are launched as pulses by generators 12, 14 in a glass or plastics sheet 10 used as an overlay for a graphical display or as the faceplate of a CRT. The time between pulses is sufficient to allow spurious reflections from the sheet edges to be damped out. An initiation signal, e.g. from a computer, from a push-button, or from closure of a switch as the tip of tranducer probe 16 is applied to sheet 10, triggers drive control 44 of the Fig. 3 circuit to gate a sine-wave signal pulse from source 46 to generators 12, 14 in turn and to start the timing. The first cycle of acoustic wave energy reaching probe 16 is sensed by detector 54 and stops the timing. Counter-timers 34 and 36 thereby register counts proportional to the probe distances from generators 12 and 14, respectively. These counts may be converted to Cartesian, polar or other coordinates if required. For providing a count directly indicating Cartesian co-ordinates, generators 12 and 14 may be replaced by two linear arrays of transducers, the arrays extending along respective, perpendicular edges of sheet 10 (Fig. 4, not shown). Details are given of a logic circuit system (Fig. 5, not shown) for controlling the following sequence: (a) the gating, at a particular point in the sine-wave cycle, of the sine-wave signal to one vibration generator, and the starting of one countertimer, (b) the stopping of the counter-timer on receipt of the acoustic pulse at probe 16 or, if the pulse is not received by the time the countertimer has reached its maximum count capacity, the re-energization of the same vibration generator for a second or further measurement attempt, (c) when a valid count has been obtained, the gating of the sine-wave signal to the second vibration generator, and the starting of the second counter-timer, (d) the stopping of the second counter-timer, or re-triggering of the second vibration generator as in b above, (e) the production of a "data-ready" signal when both counter-timers have registered valid counts. Transducer details (Fig. 2).-Generator transducer 12 is rigidly epoxybonded in sheet 10, is tubular in form, and vibrates in its length direction. The probe comprises a silvered lead zirconate titanate tubular transducer 16 (operating in a similar mode) in a flexible plastics casing 22, or cemented by soft epoxy within a rigid casing. A spherical, or hemispherical, probe tip 24 of ceramic, ruby, or sapphireprovides an approximate acoustic impedance match between the probe and sheet 10.